For the amplitude eq. (REF ) we generate symbolic expressions
of all contributing Feynman diagrams using QGRAF [1]},
and subsequently decompose them as follows:
\(\Big |\mathcal {A}^{[\text{tree}]}_{gggg} \Big \rangle &=& \sum _{i=1}^{6} \mathcal {A}^{[\text{tree}]}_{gggg}(i) ~ |c_i \rangle ~,~ \nonumber \\\Big |\mathcal {A}^{[\text{1-loop}]}_{gggg} \Big \rangle &=& \sum _{i=1}^{9} \mathcal {A}^{[\text{1-loop}]}_{gggg} (i) ~ |c_i \rangle ~,~\) 
